<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <script>
        function showHint(str) {
            var xmlhttp;
            if (str.length == 0) {
                document.getElementById("txtHint").innerHTML = "";
                return;
            }
            if (window.XMLHttpRequest) {
                // IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
                xmlhttp = new XMLHttpRequest();
            } else {
                // IE6, IE5 浏览器执行代码
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            xmlhttp.onreadystatechange = function () {
                if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
                    console.log();
                    document.getElementById("txtHint").innerHTML = xmlhttp.responseText;
                }
            }
            xmlhttp.open("GET", "../php/3.php", true);
            xmlhttp.send();
        }
    </script>
    
</head>

<body>

    <h3>在输入框中尝试输入字母 a:</h3>
    <form action="">
        输入姓名: <input type="text" id="txt1" onkeyup="showHint(this.value)" />
    </form>
    <p>提示信息: <span id="txtHint"></span></p>
    
</body>

</html>